Archer and Flynn, U.S. Pat. No. 3,361,700, disclose that a family of alkoxyalkyl esters of diiodobenzoic acid are radiopaque and suitable to plasticize vinyl resins into a form useful to manufacture tubings for catheters and similar products. Flynn, U.S. Pat. No. 3,645,955 discloses that di- and tetraiodoesters used alone or in combination with the alkoxyalkyl diiodoesters are superior for this purpose because they show less tendency to exude and lower concentrations provide a better balance between flexibility and stiffness. Burlis et al., U.S. Pat. No. 3,752,617 disclose methods for making multiwall tubing, co-tapered along its length, but make no mention of any additives, specifically by name, to produce different X-ray sensitive characteristics. Copending U.S. application Ser. No. 514,168, of Vincent J. Flynn discloses thermoplastic, e.g., polyurethane, tubing rendered non-thrombogenic with a coating layer of silicone polymer. Ostoich, U.S. Pat. No. 4,211,741 discloses a method for making a multiwall medical-surgical tubing comprising a polyvinyl chloride tubular portion and, laminated thereto via a differential-cure-temperature/rapid cooling process step, a polyurethane tubular portion.
While the iodoester opacified vinyl resin compositions of U.S. Pat. No. 3,361,700 are quite suitable for the production of tubing of simple types useful for intubation sets and catheter needles, they are not completely satisfactory for production of shaped devices. For example, if flared, or if formed into curved tips, the shapes tend to revert to straight tubing--a so-called loss of plastic memory effect. In applicant's U.S. Pat. Nos. 4,250,072 and 4,283,447, it is disclosed that such problems can be overcome if the vinyl resin is replaced partially or completely by thermoplastic polyurethane. but this tends to be expensive, especially for urethral catheters. A surface coating of silicone resin (Ser. No. 514,168) has been proposed because it helps improve ease of insertion when properly formulated, while reducing thrombogenicity, but all such constructions still can be improved, especially in terms of heat resistance and plastic memory.
More particularly, it is desirable to improve vinyl halide polymer structures in the following ways: to provide a more hydrophobic surface which allows fluid levels to be read correctly; to provide a surface with very little and, preferably, no filler exposed to minimize dangerous thrombogenic response; to provide a surface with reduced friction and wear; and to provide tubings and catheters made from such tubings which are more heat resistant and accordingly have improved sterilizability and service life.
It has now been found, and is the subject matter of the present invention, that if controlled amounts of platinum-cured silicone network polymers are employed in such compositions, tubings and catheters made therefrom will provide the above-enumerated advantages, and many others.